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Abstract

The classical nearest-neighbor Kitaev-Heisenberg model on the triangular lattice is known to host Z(2) spin vortices, forming a crystalline superstructure in the ground state. The Z(2) vortices in this system can be understood as distortions of the local 120 degrees Neel parent order of the Heisenberg-only Hamiltonian. Here, we explore possibilities of stabilizing further types of Z(2) vortex phases in Kitaev-Heisenberg models, including those which rely on more complicated types of noncollinear parent orders such as tetrahedral states. We perform extensive scans through large classes of Kitaev-Heisenberg models on different lattices employing a two-step methodology which first involves a mean-field analysis followed by a stochastic iterative minimization approach. When allowing for longer-range Kitaev couplings, we identify several Z(2) vortex phases such as a state based on the 120 degrees Neel order on the triangular lattice which shows a coexistence of different Z(2) vortex types. Furthermore, perturbing the tetrahedral order on the triangular lattice with a suitable combination of first- and second-neighbor Kitaev interactions, we find that a kagomelike superstructure of Z(2) vortices may be stabilized, where vortices feature a counter-rotating winding of spins on different sublattices. This last phase may also be extended to honeycomb lattices where it is related to cubic types of parent orders. In total, this analysis shows that Z(2) vortex phases appear in much wider contexts than the 120 degrees Neel-ordered systems previously studied.